The invention relates to a pressure compensation device that may be implanted as a prosthetic substitute for a eustachian tube.
Various diseases or malformations may be the cause that the middle ear is not ventilated enough by the eustachian tube. Patients with chronic otitis media, chronic bone suppuration, cholesteatoma or middle ear malformations often need to have the eustachian tube replaced by a corresponding prosthesis. Said prosthesis has to assume the pressure compensation otherwise provided by the eustachian tube. Such a pressure compensation device is particularly necessary with middle ear prostheses. Reference is made to the application of the same applicant filed on the same date with the title "Middle ear prosthesis". The content disclosed in said application is included in the content disclosed in the present application.
WO-A-9310729 discloses a prosthetic substitute for the eustachian tube. It describes a ventilation tube designed as a pressure compensation device for the middle ear. The ventilation tube comprises outer parts, inner parts and filter parts that are tightly connected to one another. The inner part is solidly screwed into the cranial bone. The outer part is tightly screwed on the inner part. The filter part may be plugged onto the outside located end of the outer part. The outside located side of the filter part is provided with a filter that is air-permeable but that is sealed against germs, water and the like, said filter being oriented towards the outer world.
This filter part being located outside also has to prevent the middle ear from getting soiled by dust, sand, water and the like. Its filter effect is coarse in order to protect the middle ear against infections by germs. In order to be able to protect it against water and germ penetration, the filter part has to be extremely fine pored. Due to the outside location of the filter part, the very fine pored filter runs high risks to get obstructed by coarse particles such as dirt or dust.
The object of the present invention is to provide a pressure compensation device that replaces the natural eustachian tube when latter is not able to ventilate the middle ear, whereas simultaneously the service life of the filters used and the sterility of a possible change of filter are to be improved.
The solution of this object is to provide a pressure compensation device as a prosthetic substitute for a eustachian tube with an outer part and an inner part that are tightly connected via a first tube, whereas the outer part 1. may be anchored in a bone and has a freely accessible area compared with the surrounding skin, 2. has a seat for a filter being accessible from the outside and 3. is provided with an inside connection for the first tube and whereas the inner part has a sealed housing divided into two chambers, namely into an outer chamber and an inner chamber separated from each other either by a fine filter or by a pressure compensation membrane, the outer chamber communicating with the first tube via a connection and the inner chamber being connected via a connection with a second tube ending in the middle ear.
Thanks to the pressure compensation device according to the invention, the ventilation of the eardrum, that is of the middle ear, from a head area accessible from the outside is possible. To that purpose, the outer part is inserted into the bone and is laterally surrounded by skin so that it projects outwards, being thus accessible from the outside. The technique used therefor is quite similar to the one used for bone implanted hearing aids. The outer part is preferably arranged behind the ear and covered as best as possible by the ear concha.
The outer part serves for the admission of air as well as for keeping away coarse dirt and water from the other parts of the pressure compensation device. It is therefore equipped with a filter located in a seat of the outer part and is preferably exchangeable.
The outer part is connected to the inner part via the first tube. The function of the inner part is to assure a germ-tight separation. The inner part has a housing divided into two chambers. These two chambers are either separated from each other by a highly flexible but totally impermeable membrane or they are connected to each other via a fine filter. The two chambers of the housing are designated as outer chamber and as inner chamber, the outer chamber being connected to the outer part via the first tube. The inner chamber is connected with the middle ear via the second tube, preferably with a middle ear prosthesis provided there.
The highly flexible membrane sees to it that no germs coming from the outer chamber may enter the inner chamber. The fine filter has the same function, said filter being additionally air-permeable. In order to provide the fine filter with the biggest possible filter surface, the filter is preferably designed as a hollow fiber filter. With regard to hollow fiber filters overall, reference is made to the U.S. Pat. Nos. 5,108,464 and 5,002,590 and particularly to the literature cited there.
The use of two filters (coarse and fine filter) as claimed in the present invention and more particularly the use of a coarse filter and of a highly elastic membrane protecting the middle ear against dirt and infections has considerable advantages compared with the filter arrangement in pressure compensation devices of the art:
1. The coarse filter located outside is susceptible to obstruction. It may be reached from the outside and is easily exchangeable.
2. The extremely fine pored fine filter arranged in the inner part runs high risks of obstruction by dirt. It is protected against dirt by the coarse filter arranged on the outer part. The obstruction of the fine filter is thus reliably prevented by the outside located coarse filter. The fine filter needs no more to be changed. If, instead of the fine filter, a highly flexible membrane is used for pressure compensation, the problems occurring by obstruction and described above are entirely avoided.
3. The arrangement of the fine filter inside the inner part implanted in the cranial bone protects the fine filter against any mechanical influence and thus against damage.
4. The outer part is connected to the inner part by means of a tube and said inner part is connected to the middle ear by means of another tube. This is of great cosmetic advantage. The tubes and the inner part may be implanted in the cranial bone so as not to be visible from the outside. The outer part may be freely positioned and more particularly implanted so as not to be visible from the outside.
5. As already explained under 2., the separation of coarse and fine filter increases the service life of the fine filter which has no more to be exchanged. When changing the coarse filter, which has to be done from time to time, the fine filter or the membrane always prevent germs to penetrate into the middle ear. As opposed to the pressure compensation devices of the art, the pressure compensation device according to the invention guarantees sterility during a possible change of filter.
Further advantages and characteristics of the invention will become clear in the remaining claims and in the following description of embodiments that are only examples and are not limiting the scope of the invention. Said embodiments are explained in more detail with the aid of the drawing.